Containers used for liquid or solid foodstuffs (e.g., drinking cups, containers for frozen confections and the like) are required to be substantially leak-proof so that the filled containers may be handled reliably during shipping and/or consumer usage with minimal risk of the contents leaking and thereby creating an inconvenient mess. In this regard, containers made from paperboard sheet stock material having a bottom wall glued or otherwise attached to a generally cylindrical side wall are susceptible to leakage at the circumferential seam between the bottom and side walls as well as the longitudinal seam of the side wall (i.e., where the ends of the side wall sheet are attached to one another).
Typically, therefore, paperboard container manufacturers will spot-check containers for leakage by subjecting a number of containers representing a sample of containers made during a given manufacturing run to manual leak-tests. That is, a representative number of containers for a given manufacturing run will be filled with a dyed liquid and allowed to stand for a period of time so that any leaks may be readily determined visually by the leak-test operator. If several containers from the representative sample are identified as "leakers", the cause of such defective containers is then investigated by down-time inspection of the machine which was responsible for the container manufacture. During the time that leakage problems are detected, a substantial number of potentially defective containers could be manufactured due to the high-speed operation of the container manufacturing machine thereby potentially requiring the container manufacturer to scrap an entire run of containers during that time period. Since the manufacturer cannot guarantee that all containers made during that time period are defective, there is a real risk that acceptable containers are scrapped along with any defective containers that may have been made. Clearly, such a procedure amounts to potential significant waste of resources and decreased productivity.
It has been proposed in U.S. Pat. No. 3,307,390 to Behrens et al (the entire content of which is expressly incorporated hereinto by reference) to perform leak testing of containers automatically during formation of the container's top curl. Specifically, Behrens et al disclose an apparatus whereby a separate locking member is provided as a lower component part of the curling head and is spring-biased so that the upper portion of the container side wall is compressed between the outer circumferential surface of the locking member and the upper portion of the container holder cavity. As such, the container is held in the holder cavity. (Column 4, lines 27-40.)
While the apparatus disclosed in the Behrens et al '390 patent does provide an alternative to the conventional technique of manually testing representative samples of containers for leakage, it does have some disadvantages. For example, the separate locking member which is a critical component of the structures disclosed in the Behrens et al '390 patent must be provided with a conformably sized and configured container holder. As such, the apparatus disclosed in the Behrens et al '390 patent does not lend itself to being readily retrofitted on existing container-making machinery.
It would therefore be desirable if an in-line automatic container leak testing apparatus and method were provided which could easily be retrofitted onto existing container-making machinery. It is toward fulfilling such a need that the present invention is directed.
Broadly, the present invention is embodied in a container leak-testing apparatus and method whereby the top curl forming mandrel associated with conventional container-making machinery is minimally modified so as to include a sensing port which establishes fluid-communication between the container interior and a remote pressure switch. According to the present invention, therefore, the top curl forming mandrel will capture a volume of air at the moment the top curl forming mandrel comes into contact with the top end of the container side wall. This trapped volume of air will therefore be substantially at ambient pressure. However, during the downstroke of the top curl forming mandrel into its final position, the trapped volume of air within the interior of the container will be compressed slightly in the absence of leaks. This slight increase in pressure is thereby sensed by the pressure sensor as an indication of an acceptable container.
On the other hand, if a leak is present, the downstroke of the top curl forming mandrel will not cause the ambient pressure condition within the container to increase (i.e., since the leak provide fluid-communication between the container interior and the ambient atmosphere). This lack of increased pressure condition within the container interior will likewise be sensed by the pressure sensor as an indication of a defective container.
Significantly, the testing of containers for leaks is accomplished solely by means of the volumetric compression of air trapped within the container interior during the downstroke of the top curl forming mandrel. In other words, unlike the apparatus disclosed in Behrens et al '390, no pressurizing fluid is admitted forcibly into the interior of the container during leak testing.
Upon sensing the presence of a defective container, the apparatus of this invention will activate a container transfer chute so as to remove the defective container from the container-making machinery and thereby separate it from those containers determined to be acceptable. In the event that a number of containers per predetermined unit time (e.g., at least 10 containers per minute) has been determined to be defective, the apparatus of this invention will then be placed in a self-diagnostic mode. That is, if a threshold number of defective containers per unit time is sensed, then the apparatus of this invention is capable of executing a complete machine shut-down in the event that a further predetermined number of defective containers is sensed during a subsequent unit time period (e.g., greater that 10 containers during the next successive minute of operation). If, however, no containers are determined to be defective during the next subsequent unit time period, then the controller associated with the apparatus of this invention will be reset. That is, no subsequent defective containers during a subsequent unit time period is indicative that the defective containers were simply a transient problem not associated with any inherent on-going problem associated with the container-making machine. As a result, the container-making machine is allowed to continue operation.
Further aspects and advantages of this invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments thereof which follow.